The use of hollow stem augers to take samples of soil in undisturbed soil is well known in the art. The apparatus includes a hollow stem formed by a series of pipes connected together in end-to-end relation and an inner drill rod also in the form of a series of pipes connected together in end-to-end relation. The inner drill rod is telescopically inserted into the hollow stem. Both the hollow stem and the inner drill rod are provided with cutting bits on their respective lower ends for cutting a hole in an earth formation as the apparatus is rotated by a drive mechanism located at the surface. The cutting bit secured to the inner drill rod is keyed to the cutting bit secured to the hollow stem so that both cutting bits rotate in unison. An auger is secured to the outer surface of the hollow stem for carrying cuttings to the surface.
Once the hole has been drilled to the desired depth, casing pipes can be placed in the hole to form a well wall and a gravel pack is installed around the casing pipes. Typically, the inner drill string is removed once the desired depth is achieved to allow working inside the outer casing with coring tools, soil sampling equipment, in-hole hammers, environmental monitoring equipment and other apparatus well known in the art.
Soil samples are taken every few feet during the drilling process. Heretofore, this has been achieved by telescopically removing and dismantling the entire inner drill rod from the hollow stem, inserting a soil sampling tool into the hollow stem and lowering the tool the bottom, taking a soil sample, extracting the sampling tube with its soil sample, re-assembling and lowering the inner drill rod into the hollow stem, drilling a few more feet and then repeating the process. Clearly, this has been a time consuming process, particularly when the bore hole is several hundred feet in depth. This arrangement also suffers from the disadvantage that, with the removal of the prior art pilot bit, there is nothing to prevent formation heaving, that is, sand flowing into the auger bit and beyond as a result of differential pressures and water flow. Severe instances of formation heaving can prevent re-installation of the pilot bit. Notwithstanding these disadvantages, the above-described auger bit assembly provides sufficient advantages to warrant continuing with its relatively widespread use. There is clearly a need for an apparatus which will speed up the soil sampling process.